Outdoor enclosures that contain high-power electronic components require a method to dissipate the heat generated by the electronic components. At the same time, it is often required that the electronic components be enclosed in a sealed enclosure to protect the electronic components from the outside environment. Typically, the high power components are attached to a heat sink. The heat from the electronic components travels through the heat sink and the outer surface area creates a natural convection via the heat sink fins to dissipate the heat.
In some cases, the high-power electronic components dissipate too much heat for natural conduction to remove all the heat at all times. In this case, fans and a fan shroud can be employed to cover the entire outer surface of the heat sink and drive forced air between the fins to increase the volumetric air flow, thus increasing the cooling capacity of the heat sink. The fan shroud cover is necessary to keep the forced air between the fins, but limits the fins ability to cool via natural convection if the ambient temperatures are low enough. This solution requires the fans to run at all times, even when the ambient conditions are cool enough for an un-shrouded heat sink to be capable of cooling the electronic components without a fan. The continuous use of the fans is power consuming. Continuously-used fans need repair or replacement more often than intermittently-used fans. The running fans also generate audible noise. To some extent, the shroud that is required to keep the fan-forced air against the outer surface of the heat sink acts as a barrier to natural convection.